This invention relates to a method of cooling hot gases containing solids, tar and naphthalene wherein the hot gases are treated with a cooling fluid in a direct condenser to cool the gases. More particularly, the present invention relates to such a method wherein the cooling fluid is purified in a circuit for recycling to treat further quantities of gas.
In many gasification and degasification processes, particularly the destructive distillation process occurring during the coking of coal, gases are liberated containing tar and naphthalene. Frequently, the gases also contain solids, such as carbon black and mineral salts. When such gases are cooled in heat exchangers having stationary cooling surfaces, the tar, naphthalene and solids are deposited mainly on the cooling surfaces. These deposits foul and clog the heat exchanger. As a result, the heat exchanger devices must frequently be taken out of operation and cleaned. Usually the heat exchangers are made much larger than necessary to insure long periods of operation.
To avoid the disadvantages of fouling and clogging of the stationary cooling surfaces in heat exchangers, sometimes also referred to in the art as gas condensers, the hot gases are brought into direct contact with a cooling fluid, usuallywater in a direct gas condenser. The cooling fluid contacts the gases without the use of cooling surfaces because they become readily fouled.
Direct gas condensers, as they are usually referred to in the art, operate for relatively long periods of time and do not need to be excessively large in size. Usually, the cooling water which has been heated in the direct gas condenser is collected after traveling through the condenser. The collected cooling water is pumped to one or more circulating condensers where the water is cooled until it can be recycled to the direct gas condenser. However, substances, such as gas condensate, solids, tar and naphthalene, are withdrawn from the gases undergoing cooling and accumulate in the circulating cooling water. The accumulation of such substances interferes with the operation of the circulating condensers and the nozzles used in the direct gas condenser. Consequently, part of the circulating cooling fluid must be continuously withdrawn and purified.
It is another known method in the art to reduce the amount of circulating fluid which has to be washed or purified by using a tar separator in the cooling fluid circuit whereby tar and solids are separated from the circulating water by settling to achieve phase separation. The tar and solids are thus removed from the circuit by the separator. This known method does not eliminate fouling of the circulating condenser. Usually, the circulating condenser is divided into a number of individually-switchable condenser devices or units so that a condenser unit or device can be cleaned without eliminating entirely the circulating condenser function in the circuit.
It is also known to introduce additional quantities of tar into the circuit wherein the tar partially dissolves the naphthalene incrustations in the circulating condensers, thus prolonging the periods of operation by the condensers. However, the practical effect of adding tar to the circuit is limited.